In a computer system, when data of a migration source volume managed by a migration source storage apparatus is migrated to a migration destination volume managed by a migration destination storage apparatus, a first access path linking the host computer to the migration source volume is switched to a second access path linking the host computer to the migration destination volume after the data has been migrated from the migration source volume to the migration destination volume. Here, according to the prior art, when the switch is made from the first access path to the second access path, temporary suspension of host access in which the host computer accesses the migration source volume or migration destination volume is unavoidable. The following two points may be given as reasons for why this is the case.
First, the migration source volume and migration destination volume each have different device manufacturing numbers and other configuration information, and therefore, following migration from the migration source volume to the migration destination volume, the host computer is required to re-identify the migration destination volume.
Meanwhile, in order to migrate the data of the migration source volume to the migration destination volume while continuing host access, consideration has been given to switching access paths while still continuing host access by configuring a plurality of access paths between the host computer and the migration source volume, configuring a plurality of access paths between the host computer and the migration destination volume, and switching each access path in stages from the migration source volume to the migration destination volume. However, because the access path linking the host computer to the migration source volume and the access path linking the host computer to the migration destination volume are generated in parallel, if write access by the host computer occurs during data migration, only the data of one volume of the migration source volume and migration destination volume is updated and data consistency between the migration source volume and migration destination volume can no longer be maintained.
Methods have therefore been proposed for migrating the data of the migration source volume to the migration destination volume without halting host access (see PTL 1 and PTL 2). According to PTL 1 and PTL 2, the first access path linking the host computer to the migration source volume and the second access path linking the host computer to the migration destination volume are configured as alternate paths and the data of the migration source volume is migrated to the migration destination volume after switching the alternate path from the first access path to the second access path.
At this time, prior to data migration, the first access path is made active and the second access path is placed on standby, and when the alternate path is switched from the first access path to the second access path, the first access path is made active and the second access path is made active, and if the data of the migration source volume is migrated to the migration destination volume after the alternate path has been switched from the first access path to the second access path, the first access path is placed on standby and the second active path is made active. When the first access path and the second access path are placed in an active or standby state, the first access path and second access path are both made active at the stage where the alternate path is migrated from the first access path to the second access path.
Hence, if write access from the host computer to the migration source volume occurs while the alternate path is being switched from the first access path to the second access path, update data is stored in the migration source volume, but if write access to the migration destination volume by the host computer occurs, the update data is not stored in the migration destination volume, rather, update data is stored only in the migration source volume.
Meanwhile, during data migration, the first access path is on standby and only the second access path is active. In this case, if write access by the host computer to the migration destination volume occurs, in PTL 1, the write data is merged with the data which is read from the migration source volume and the merged data is written.
Meanwhile, according to PTL 2, if write access to the migration destination volume by the host computer occurs, update data is always stored in the migration destination volume and update data is also stored in the migration source volume. In this case, in order to duplex the data, the end of processing is reported to the host computer after the update data has been written to the migration destination cache memory and then the update data is copied to the migration source volume.